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Tilted Orbit Of Exiled Planet Around Binary Star Linked To Stellar Flyby 3 Million Years Ago

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Objects in the solar system with weird orbits have been linked to a close encounter with another star during our stellar system's infancy.

Findings of a new study suggest stellar flybys can indeed knock planets, comets, and asteroids off balance and reshape planetary systems.

HD 106906

Paul Kalas, from UC Berkeley, studies young, newly formed planetary systems to understand what happened in the early days of the solar system. He studied a star system, which lies about 300 light years away from Earth and is very young at only about 15 million years old.

The star system has a massive planet in a highly unusual orbit. The planet, HD 106906 b, is 11 times more massive than Jupiter and orbits the binary star HD 106906 in an orbit tipped about 21 degrees from the plane of the disk around the star.

Using the Gemini Planet Imager on the Gemini Telescope and data from the Hubble Space Telescope to get a closer look at HD 106906, Kalas also found the binary star has a lopsided comet belt.

HD 106906 b's strange orbit and the dust disk being asymmetrical suggest something disrupted the system.

What Caused 106906 b's Strange Orbit

Kalas and his colleague Robert De Rosa, a research scientist at Stanford's Kavli Institute for Particle Astrophysics and Cosmology, proposed the planet may have been kicked out of its solar system by interactions with a yet-to-be-seen planet in the system or by a passing star.

The researchers think both scenarios happened. The planet may have been kicked into an eccentric orbit after a close encounter with a central binary star. Repeated gravitational kicks from the binary may have ejected the planet into interstellar space, but the passing stars nudged the planet's orbit into a safer distance from the binary.

To test their hypothesis, the researchers used data from the Gaia space observatory, which collects information such as the distance, position, and motion of 1.3 billion stars in the Milky Way.

After gathering data on 461 stars in the same cluster as HD 106906, the researchers calculated the positions of these objects backward in time. This revealed that another binary star system may have approached close enough 3 million years ago, altering the planetary system.

"What we have done here is actually find the stars that could have given HD 106906 b the extra gravitational kick, a second kick so that it became long-lived, just like a hypothetical Planet Nine would be in our solar system," Kalas said. "We started with 461 suspects and discovered two that were at the scene of the crime."

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